1. Field of the Invention
The field of this invention generally relates to footwear, and more particularly to an article of footwear having a system for providing cushioning and support for the comfort of the wearer.
2. Background Art
One of the problems associated with shoes has always been striking a balance between support and cushioning. Throughout the course of an average day, the feet and legs of an individual are subjected to substantial impact forces. Running, jumping, walking and even standing exert forces upon the feet and legs of an individual which can lead to soreness, fatigue, and injury.
The human foot is a complex and remarkable piece of machinery, capable of withstanding and dissipating many impact forces. The natural padding of fat at the heel and forefoot, as well as the flexibility of the arch, help to cushion the foot. An athlete's stride is partly the result of energy which is stored in the flexible tissues of the foot. For example, during a typical walking or running stride, the achilles tendon and the arch stretch and contract, storing energy in the tendons and ligaments. When the restrictive pressure on these elements is released, the stored energy is also released, thereby reducing the burden which must be assumed by the muscles.
Although the human foot possesses natural cushioning and rebounding characteristics, the foot alone is incapable of effectively overcoming many of the forces encountered during athletic activity. Unless an individual is wearing shoes which provide proper cushioning and support, the soreness and fatigue associated with athletic activity is more acute, and its onset accelerated. This results in discomfort for the wearer which diminishes the incentive for further athletic activity. Equally important, inadequately cushioned footwear can lead to injuries such as blisters, muscle, tendon and ligament damage, and bone stress fractures. Improper footwear can also lead to other ailments, including back pain.
Proper footwear should complement the natural functionality of the foot, in part by incorporating a sole which absorbs shocks. However, the sole should also possess enough resiliency to prevent the sole from being “mushy” or “collapsing,” thereby unduly draining the energy of the wearer.
In light of the above, numerous attempts have been made over the years to incorporate into a shoe means for providing improved cushioning and resiliency to the shoe. One concept practiced in the footwear industry to improve cushioning and energy return has been the use of fluid-filled devices within shoes. For example, U.S. Pat. Nos. 5,771,606, 6,354,020 and 6,505,420 teach such devices. These devices attempt to enhance cushioning and energy return by transferring a fluid between the area of impact and another area of the device. The basic concept of these devices is to have cushions containing fluid disposed adjacent the heel or forefoot areas of a shoe which transfer fluid to the other of the heel or forefoot areas. Several overriding problems exist with these devices.
One of these problems is that often the fluid filled devices are permanently embedded into the sole of the shoe and, therefore, not adjustable. For example, shoes can be made to adjust for the various lengths of feet, but it is impossible for the shoe industry to account for variations in the weight of the wearer. Further, it may be desirable to adjust the amount of cushioning and support for various activities such as running, biking, or casual walking. In addition, the level of performance may change the type of cushioning and support sought by the wearer. For example, an athlete may choose to have a different amount of support while training than while competing. Consequently, it is desirable to have the amount of air (or the pressure) within the sole be adjustable.
Adjusting fluids in the sole of footwear is known in the art of footwear design. For example U.S. Pat. No. 4,610,099 to Signori (the Signori patent) shows a shoe having an inflatable bladder in the sole. The Signori patent provides for the bladder to be inflated using a hypodermic needle insertion.
Another difficulty for shoe designers is to design one insert that is right for every foot. This task is almost impossible because the shape and contour of each foot and the way each foot applies pressure to the sole of a shoe varies dramatically. For example, because the heel is the first part of the foot to hit the ground during the typical gait of a human, many designs show a large fluid filled chamber in the heel portion of an insert for harsh pressure forced downward by the heel. However, the shape of a heel is not the same for everyone nor is the way the heel provides pressure to the sole of a shoe. If the pressure from the heel does not hit the large fluid filled chamber in the right way, a consistent support is not provided. For example, if the heel lands on the sole slightly off-center, the heel chamber is limited in the way it can deform when the weight of the heel is pressed against it. Consequently, one large heel chamber will not provide proper support to each and every foot.
An additional problem with the shoe inserts formerly described is that in order to provide support, the insert often lacks flexibility. Large air filled bladders when fully inflated, have only a limited ability to longitudinally and laterally flex with the movement of the foot and/or shoe.